Tooling systems for composite manufacturing may include surfaces for bonding composites in an autoclave or oven. In the autoclave, the bonding tool and the part to be cured are brought up to the curing temperature required to cure the matrix or resin. The tool must be designed so that its tool surface provides the desired part shape or mold surface profile at the bonding temperature. The thermal expansion of the bonding tool must be taken into account. If the tool has a low coefficient of thermal expansion (CTE), then it will be easier to machine the tool at its ambient temperature and ensure the proper mold surface profile in its thermally expanded state at the bonding temperature. Also, a low CTE of the bonding tool can contribute to preventing spring back in the cured part. Thus, a low CTE is generally recognized as desirable for a composite bonding tool to be used in an autoclave or oven.
A bonding tool with either of or a combination of a low thermal conductivity and a high mass is general undesirable. Low thermal conductivity and/or a high mass contribute to a low heating rate. The bonding tool must be relatively uniformly heated in the autoclave or oven to avoid part distortions and potential spring back. If the heat rate is low, then the autoclave or oven must be brought to the curing temperature slowly, which contributes to a long cycle time for the cure. Thus, a high heat rate achieved by high thermal conductivity and/or low mass is also recognized as generally desirable for a composite bonding tool.
Bonding tools may be made from nickel-iron based alloys, such as the nickel-iron alloy available under the trade name INVAR. Advantageously, the nickel-iron alloys may have a low CTE and are relatively durable. However, they also have a relatively low thermal conductivity when compared to other metals, and they are heavy in addition to being relatively difficult to machine.
Metal matrix composites, ceramics, and sintered materials have each been proposed as materials to form composite bonding tools with properties different from, and in some cases more advantageous than nickel-iron based alloys. However, each one also suffers from certain drawbacks such as durability and cost. A new, improved material for forming a composite bonding tool with a low CTE, and a high heat rate (through low mass and/or high thermal conductivity) is desired.